This invention relates to a drive for a rolling shutter of the type which is suspended beneath a generally horizontally extending track and which travels on a linear or non-linear path extending horizontally. Such a shutter may be for example of the type set out in our prior British patent number 2I84474.
In that patent, there is described and claimed a horizontally moving shutter which, when fully stowed away, is rolled about a vertical barrel. It is driven by a motor acting on a drive sprocket at the barrel and is pushed out from the barrel housing along the track. The shutter curtain is tensioned throughout its movement by a substantially constant tension spring arrangement which also assists in returning the shutter to the barrel when it is being stowed.
It has been found possible by this means to drive extremely large shutters, up to 30 meters in length.
However, there is a problem with driving a shutter of this type over a longer distance or with driving a shutter of substantial length around a very circuitous track which has a tendency to increase the friction met by the shutter. Clearly, it is undesirable to overstrain the drive motor. However, increasing the horsepower of the drive motor is not the answer to the problem of extending the shutter further.
It has been proposed to attach a motor to the far end of the track and, by means of cables to pull the shutter into its extended fully opened condition but this is most unsatisfactory because the cable needs to be guided around the track if there are any bends in the track and also tends to sag along its length, stretch in use and otherwise cause problems.
It would be desirable to provide an auxiliary drive such that, at a predetermined distance from the barrel housing, the leading end of the shutter is engaged by the auxiliary drive and is driven forwards in addition to the continuing operation of the main drive motor. Although this would be desirable, hitherto no means has been found of engaging an auxiliary drive motor with the leading end of the shutter in motion.
It will be appreciated that a metal rolling shutter of perhaps 30-40 meters in length has a very substantial mass and, even when moving at a relatively slow speed, has very substantial momentum. In an attempt to engage a drive with such a moving shutter, it is essential to ensure that the auxiliary drive engages the shutter cleanly at the appropriate position without obstructing its passage. Otherwise there is a danger of either jamming the shutter or damaging the auxiliary drive or both. It is also essential to synchronise the auxiliary and main drives.